Telephone system



Sept. 17, 1946. .1. H. Voss TELEPHONE SYSTEM Filed June 24, 1958 6 Sheets-Sheet l nr?` Hass l l )"M AwmRmsY.

Jahn BY my@ W47 l f 6 Sheets-Sheet 2 J. H. VOSS TELEPHONE SYSTEM Filed June 24, 1958 lDI Sept. l 7, 1 940.

Sept. 17, 17940. 1. H. Voss 2,214,914

TELEPHONE SYSTEM l Filed June 24, 19258 6 Sheets-Sheet 5 Fi g1 3 l INVENTOR. l l Jahn Unas ATTORNEY.

Sept'. 17, 1940. J. H. VOSS 2,214,914/

TELEPHONE: SYSTEM Filed June 24, 1938 6 Sheets-Sheet 4 l C F.. 4 @4758 74806 H4776 -||5r 0864/0638,

gwas l C802 INVENTOR.

BY Jahn Herzt1 Unss gm' Qn/UJI j I 1 -L ATTORNEY.

Sept. 1 7, 194C. J. H. voss- TELEPHONE SYSTEM 6 Shets-heet 5 Filed June 24, 19558 INVENTOR Jul-Ln HEI-Lr` ATTORNEY.

Sept. 17, 1940. J. H. Voss K TELEPHONE SYSTEM Filed June 24, 1958 6 Sheets-Sheet 6 .i l50 thereto.

l Patented Sept. 17, 1940 UNITED STATES- PATENT OFFICE TELEPHONE SYSTEM John H. Voss, Downers Grove, Ill., asslg'nor to Associated Electric Laboratories, Inc., Chicago, Ill., a corporation oi' Delaware Application June 24, 1938, serial No. 215,517

34 claims. (cl. 179-27) B. X. conventionally comprises an attendant cabinet or operator station, a number of subscriber substations, a plurality of two-way-trunk lines extending between the P. A. B. X. and a central ex'- change associated therewith, a plurality of subscriber lines individually extending to the subscriber substations, and apparatus including a switch train having access to each of the subscriber and trunk lines which is operated to set up connections between the various subscriber and trunk lines. Usually the apparatus in a P. A. B. X. of this type is so connected and arranged that the connections between the various n subscriber lines can be set up by the subscribers at the subscriber substations without the assistance of an attendant at the attendant cabinet. Frequently the apparatus is also connected and arranged so that a subscriber at one or more of the subscriber substations can initiate an outgoing central exchange call from the P. A. B. X. on an idle one of the trunk lines without the assistance of the attendant at the attendant cabinet. Universally, when the attendant is on duty,

30 incoming central exchange calls to the P. A. B. X.

l, 85 provided with a night switch or key which is operated before the attendant leaves the attendant cabinet or goes off duty in order to institute night service. In a conventional P. A. B. X., this operation of the night key at the attendant cab- 40 inet sets up connections between the trunk lines extending to the P. A. B. X. and corresponding ones of a selected number of the subscriber lines, whereby incoming central exchangecalls to the P. A. B. X. on the trunk lines are automatically 45 routed to the corresponding selected subscriber substations.

While reasonably satisfactory service4 may be rendered the subscribers in a P. A. B. X. of this type, there are several objectionable features In the first place, the attendant frequently leaves the attendant cabinet for several minutes at a time without operating the night key, thereby rendering the P. A. B. X. totally without incoming central exchange call service 55 during this time'interval. Also, when night service is in force, an incoming central exchange call to the P. A. B. X. must be answered at the particular selected subscriber substation. which is associated with the subscriber line connected to the particular trunk line over which the central 5 exchange call is routed. Moreover, al1 incoming central exchange calls to the P. A. B. X., when night service is in force, must be answered at one of several selected rsubscriber substations.

Furthermore, an incoming-central exchange call 1f" to the P. A. B. X. will be routed thereto by way oi the second-choice trunk line extending thereto if the first-choice trunk line extending thereto is y busy at the time, rendering it impossible to answer change call is not answered at the operator station /Within a predetermined time interval. Another object of the invention is to provide,

in a private exchange of the character noted including an operator station and a plurality of subscriber substations, an arrangement for automatically rendering the apparatus at each oi Y the subscriber substations independently operative to answer an incoming central exchange call to the private exchange in the event the incoming central exchange call is not answered at the operator station within a predetermined time interval.

Another object of the invention is to provide, in a private exchange of the character noted including an operator station, a plurality of sub-- scriber substations and an automatic switch operative to seize an assigned one of a number of trunk lines extending to the P. A. B. X., a device at each subscriber substation operative to cause "operation of the automatic switch and an iin'- proved arrangement for controlling the assignment of the trunk lines.

A further object of the invention is to' provide, 50 in a private exchange of the character'noted in.- 'cluding an'operator station'and a plurality of subscriber substations, a device at the operator station which is operative to render eilective the apparatus at each of the subscriber substations to answer an incoming central exchange call to the private exchange.

It is a further object of the invention to provide, in a private exchange of the character noted including an operator station and a plurality of subscriber substations, a device at the operator station and an arrangement controlled jointly by the operation of the device and the extension of an incoming call to the private exchange on any one of the trunk lines for rendering eective the apparatus at each of the subscriber substations to answer an incoming central exchange call to the private exchange and for causing ringing current to be projected over at least a number of the subscriber lines. y

The features of the present invention are illustrated as being incorporated in a P. A. B. X. including an attendant cabinet or operator station, a number of each of three different classes of subscriber substations, a plurality of two-way trunk lines extending to the P. A. B. X. from a central exchange associated therewith, a plurality of subscriber lines individually extending to the subscriber substations, an information trunk extending to the attendant cabinet, a number of local links for setting up connections between the various subscriber lines, a number of trunk circuits individually associated with the trunk lines for setting up connections between the various trunk and subscriber lines, and an allotter for controlling the assignment of the local links and trunk circuits to the use of the subscriber substations. The classes of subscriber substations comprise authorized, semiauthorized and unauthorized subscriber substations, these classifications being indicative of the character of the service rendered thereto, as is more fully explained subsequently. Each of the local links comprises a finder switch or portion and a connector switch or portion, the nder switch having access to each subscriber line and the information trunk, and to a plurality of link lines individually associated with the trunk circuits, and the connector switch having access to each subscriber line and the information trunk. Each trunk circuit individually associated with a trunk` line extending to the P. A. B. X. individually comprises a trunk finder-connector switch having access to each subscriber line extending to an authorized or semiauthorized subscriber sub station in the l?. A. B. X.

In accordance with one feature of the invention, the private exchange includes an operator station and at least one subscriber substation, a trunk line extending to the private exchange, normally effective apparatus at the operator station operative to answer an incoming call to the private exchange on the trunk line, normally ineiective apparatus at the subscriber substation operative to answer an incoming call to the private exchange on the trunk line, and automatic means operative inthe event an incoming call to the private exchange is not answered within a predetermined time interval by the operation of the apparatus at the operator y station for rendering effective the'apparatus at "the subscriber substation.

In accordance with another feature of the invention, the private exchange includes a plurality of subscriber substations, a plurality of trunk lines extending to the private exchange, normally ineffective apparatus at 4each of the subscriber substations operative to answer an incoming call to the private exchange on any one of the trunk lines, and automatic means operative in the event an incoming call to the priva exchange on any one of the trunk lines is not answered within a predetermined time interval by the operation of the apparatus at the operator station for rendering effective the apparatus at each of the subscriber substations.

In accordance with another feature of the invention, there is provided a device at each subscriber substation, normally eiective means responsive to the operation of the device at any one of the subscriber substations for causing an idle one of the trunk lines to be associated with the one subscriber substation, normally ineffective means responsive to the operation of the device at any one of the subscriber substations for causing one of the trunk lines having an incoming call to the private exchange thereon t be associated with the one subscriber substation, and automatic means operative in the event an incoming call to the private exchange on any one of the trunk lines is not answered Within a predetermined time interval by the operation of the apparatus at the operator station for rendering ineffective the rst-mentioned means and for rendering effective the last-mentioned means. More particularly, the P. A. B. X. comprises an automatic switch operative to set up a connection between the various trunk and subscriber lines, and an allotter including a switch having normal and off-normal positions. The allotter is so constructed and arranged that when the switch occupies its normal position an idle trunk line is assigned to be included in a connection to be set up, and when the switch occupies its off-normal position a trunk line having an incoming call to the P. A. B. X. thereon is set up to be included in the connection. A timer is provided which is set into operation when an incoming call is extended to the P. A. B. X. on any one of the trunk line's, the operation of this timer being arrested when the call on the one of the trunk lines is answered by the operation of the apparatus at the operator station. In the event the timer operates for a predetermined time interval, it is effective to cause the switch to operate from its normal to its olf-normal position. The operation of the device at any one of the subscriber substations is eifective to cause the automatic switch to set up a connection between the subscriber line extending to the one subscriber substation and an assigned trunk line.

In accordance with a further feature of the invention, a device is provided at the operator station which is operative to render the apparatus at each of the subscriber substations effective to answer an incoming call to the private exchange on any one of the trunk lines. More particularly, this operation of the device at the operator position conditions the switch in the allotter to be operated from its normal to itsl olf-normal position, this switch being operated from its normal to its off-normal position when an incoming call is extended to the private exchange.

In accordance .with a further feature of the invention, the private exchange comprises lan r arrangement controlled jointly by the operation of the device at the operator station and the` the subscriber lines. More particularly. the operation of the device at the operator station conditions a relay to be operated, which relay is operated when an incoming call is extended to'the P. A. B. X. Upon operating. the relay operates the switch in the allotter from its normal to its oit-normal position and completes a path for projecting ringing current over at least a number of the subscriber lines.

Further features of the invention pertain to the particular arrangement of the circuit elements thereof, whereby the above-outlined and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the vappended claims. The invention, l,both as to its organization and method of operation, together with further objects and' advantages thereof, will best beA understood by reference to the following specification, taken in connection with the accompanying drawings, vin which Fig. 6

DescriptionV of the apparatus incorporated in the telephone system Referring now more particularly to Fig. 6 of the drawings, the telephone system there illustrated comprises a P. A. B. X. I0, a central exchange 20, and a plurality of two-way trunk lines 2|, and an allotter 50 for assigning the local links and trunk lines to the use of the subscriber s ubstations. The number of local links and trunk lines employed is determined by the volume and character of the trailc to be handledjby the P. A. B. X., and reasonable service can be rendered in a P. A. B. X. of this character when three local links and three trunk lines are provided. The rst local link 2| comprises a finder portion or switch 22 and a connector portion or switch 23; and the first trunk line |005 is individually provided with a trunk circuit 60 including a trunk finder-connector switch 30 individual thereto. A subscriber line and a line circuit individual thereto are associated with each subscriber substation, the subscriber lines 40|, 402 and 403 being respectively associated with the subscriber substations C, B and A. Also, an information trunk 650 and a line circuit individual thereto are associated with the attendant cabinet 40.

The finder switch 22 of the first local link 2| and each of the other finder switches of the local links have access to each subscriber line, to the information trunk, and to a link line individually associated with each trunk circuit, the link -line 830 being individually associated with the first trunk circuit 60. The' connector switch 23 ofthe local link 2| and each of the other connector switches of the local links have access, by way of a trunk line 200, to each subscriber line and to the information trunk. 'I'he trunk finderconnector switch 30 of the rst trunk circuit 60 and each of the other trunk finder-connector switches of the other trunk circuits have access to the authorized and semlauthorized subscriber lines.

Preferably. the attendant cabinet 40, as shown to the left of the dashed line in Fig. 3, comprises a telephone instrument including a transmitter 565 and a receiver 566 associated with a voice current repeater 511, a dialing mechanism 582 and a group of control switches. 'I'he repeater 511 is associated with the line conductors ofv a trunk line at the attendant cabinet 40 by way of an impedance 500, and talking battery current is supplied to the telephone instrument at the attendant cabinet 40 by way of an impedance 520. The information trunk 650 extends to the attendant cabinet 40 and is provided with a signal 56| and a line circuit including a combined line and cut-ofi' relay R200. An impulsing relay R5|0 is associated with the dialing mechanism 582 and a number of control relays R530, R540 and R550, a thermostatic device T510 and a trunk signal buzzer M516 are commonly assoelated with-the trunk circuits terminating at the attendant cabinet 40.

The group of control switches provided at the attendant cabinet 40 comprises a trunk release switch 590, a. grounding switch 560, and a night switch 510 commonly associated with the trunk circuits terminating thereat, and a trunk hold switch, a connect switch and a dial-split switch individually associated with each trunk circuit terminating thereat, the trunk hold switch 563, the connect switch 600 and the dial-split switch 6|0 being individually associated with the first trunk circuit 60. Also, an answer and supervisory lamp is individually associated with each'trunk circuit terminating at the attendant cabinet, the answer and supervisory lamp 564 being individually associated with 'the first trunk circuit 60. Also, an information trunk switch 593 is individually associated with the information trunk B and a trunk switch 561 is individually associated with the trunk signal buzzer M516.

Each of the subscriber substations is provided with a telephone instrument, va ringer and a line circuit associated with the subscriber line extending thereto. Each of the line circuits comprises a combined line and cut-ofi.' relay, the combined line and cut-oil? relays includes in the line circuits individually associated with the subscriber lines 40|, 402 and 403 being respectively indicated at R310, R380 and R390 in Fig. 2. 'I'he telephone instrument of each of the authorized subscriber substations has associated therewith a grounding push button which is operative to apply direct ground potential to the line conductor of the subscriber line extending thereto, the grounding ypush button associated with the telephone instrument at the telephone substation A being indicated at 393. Also it is noted that the receivers of thetelephone instruments at the authorized subscriber substations are of the permanent magnet type, for a purpose more fully described subsequently. Also, a control relay is individually associated with each of at least a selected number of the authorized subscriber substations, this control relay individually associated with the authorized subscriber substation A being indicated at R430.' rI'hese control relays are controlled by a common relay R420 in order to cause coded ringing current to be projected overl the corresponding subscriber lines, when night service is in force and an incoming central exchange call is extended to the P. A. B, X., in a manner more fully described subsequently. Also, a general incoming trunk signal 381 is commonly associated with the authorized subscriber substations which is operated when temporary direct answering of incoming central exchange calls to the P. A. B. X. is in force.

Preferably, each of the local links is connected and arranged in a manner similar to that of the link 1ine'2|; and the latter local link comprises, as shown in Fig. l, in addition to the finder switch 22 and the connector switch 23, an impulsing relay R|30, a hold relay RVI40, a ring cut-off relay R|20, and a number of control relays R|00, RI |0 and R|50. Operatively connected to the finder switch 22 is a motor M|1|, and operatively connected to the connector switch 23 is a motor M |10, these motors preferably being connected to the corresponding switches by a pawl and ratchet mechanism (not shown). Also, the local link 2| includes a thermostatic device T|60 which is operative in the event the first local link fails to find a calling subscriber line within a predetermined time interval to cause the second local link to hunt for the calling subscriber line.

- The nder switch 22 comprises four rotary switches, 260, 264, 268 and 212, each including a contact bank and an associated wiper, the contact banks being respectively indicated at 262, 266, 210 and 214, and the associated wipers being respectively indicated at 26|, 265, 269 and 213. Preferably, the contact bank of each rotary switch includes twenty-five contacts, and the associated wiper .thereof is of the double-ended type. The rotary switches 260, 264 and 212 respectively terminate the negative, positive'and general control conductors of the subscriber and link lines and the information trunk. The l'rotary switch 268 terminates the special control conductors of the link lines. More particularly, the subscriber lines terminating at the rotary switches 260, 264 and 212 are arranged in three groups, the first group utilizing the contacts between 1 and 9, the second group utilizing the contacts between 11 and 19, and the third group utilizing the contacts between 21 and 23 in the contact banks of these rotary switches. The link lines terminating at the rotary switches 260, 264, 268 and 212 utilize the tenth, twentieth and twenty-fifth contacts in the contact banks of the switches. The information trunk 650 utilizes the twenty-fourth contacts in the contact banks of the rotary switches 260, 264 and 212.

The connector switch 23 comprises live rotary switches, 240, 244, 248, 252 and 256, each including a contact bank and an associated wiper, the contact banks being respectively indicated at 242, 246, 250, 254 and 258, and the associated wipers being respectively indicated at 24|, 245, 249, 253 and 251. Preferably, the contact bank of each rotary switch includes twenty-live contacts and the associated wiper thereof is of the double-ended type. The rotary switches 248, 252 and 256 respectively terminate the general control, positive and negative conductors of the subscriber lines and information trunk. The rotary switch 240 is utilized in returning the connector switch 23 to its home position, all of the contacts in the contact bank thereof with the exception ofthe twenty-fth contact being multipled together. The rotary switch 244 terminates trunk nder switches of the trunk circuits. As

previously noted, the subscriber lines terminating at the rotary switches 248, 252 and 256 are arranged in three groups, the firstgroup utilizing the contacts between 1 and 9, the second group utilizing the contacts between 11 and 19, and thev third group utilizing the contacts between 21 and 23 in the contact banks of these rotary switches.` The tenth, twentieth and twenty-fifth contacts in the rotary switches 248, 252 and 256 are utilized for control purposes in a manner more fully explained. subsequently. The information trunk utilizes the twenty-fourth contacts in the contact banks of the rotary switches 248, 252 and 256.

From the foregoing it is apparent that the directory numbers of the subscriber lines in the first, second and third groups respectively comprise the numbers between 1 and 9, 01 and 09, and 001 and 003, and that the directory number of the information trunk comprises the number 004.

nected and arranged in a manner similar to that of the first trunk circuit 80, the latter trunk circuit comprising, as shown in the Figs. 3, 4 and 5, a -plurality of trunk conductors, the trunk finderconnector switch 30, and a group of relays and a group of thermostatic devices for controlling the operation of the rst trunk circuit. This group of relays comprises two impulsing relays R and R190, a hold relay R110, a ring cut-off relay R160, two differential relays R900 and R9 0, two ringing relays R1|0 and R980, four switching relays R120, R140, R920 and R940, and a plurality of control relays, R130, R150, R180, R905,

R930, R950, R960 and R910. The group of thermostatic devices comprises the thermostatic devices indicated at T805, T8|0, T8|5, T962 and T964.

Certain auxiliary wiring is provided, including the wiring illustrated at X, Y and Z. which is connected in a manner more fully described subsequently, in order to accommodate the use of the P. A. B. X. in connection with a central exchange of the automatic, common manual battery or manual local battery types. The X wiring comprises a connection between the lower terminal of the lower winding of the relay R960 and the armature RA911 of the relay R910, and a connection between the contact associated with the armature RA911 and the positive trunk conductor |0| The Y Wiring comprisesl a con- Preferably, each of the trunk circuits is connection between the lower terminal of the win'ding of the thermostatic device T8|5 and the armature TA8|6 thereof. The Z wiring comprises a connection in multiple to the contacts controlled by the armature RA92| of the relay R920, a connection in multiple to the contacts controlled by the armatures RA923 of the relay R920, a connection between the contact controlled by the armature RA945 of the relay R940 and the contact controlled by the armature RA914 of the relay R910 and a connection between the armature RA914 and the upper terminal of the winding of the relay R980. When the central exchange is of the automatic type, only the X" wiring illustrated is connected; when the central exchange is of the manual common battery type only the X" and Y wiring illustrated are connected; and when the central exchange is of the manual local battery type only the X and Z wiring illustrated are connected. Also, the auxiliary wiring illustrated at A and comprising a connection in multiple to the contacts controlled by the armature RA941 of the relay R940 is pro- 75 vided for the purpose of facilitating the transfer of a central exchange connection back and forth between two authorized subscriber substations, in a manner more fully described subsequently.

The trunk finder-connector switch 30 comprises ilve rotary switches 610, 614, 618, 682 and 606, each including a contact bank and an associated wiper, the contact banks being respectively indicated at 612, 616, 680, 634 and 688, and the associated wipers being respectively indicated at 61|, 615, 619, 683 and 681. Operatively connected to the trunk nder-connector switch 30 is a motor M6I5, this motor preferably being connected to the switch by a pawl and ratchet mechanism (not shown). Preferably, the contact bank of each rotary switch includes twenty-five contacts, and the associated wiper thereof is of the doubleended type. The rotary switches 618, 682 and 686 respectively terminate the general control,4 positive and negative conductors of the authorized and semiauthorized subscriber lines. The rotary switch 614 terminates the control conductor extending to the connector switch 23 of the local link 2|, and the corresponding conductors extending to .the connector switches of the other local links. 'The rotary switch 610 is utilized in returning the trunk ilnder-connector'switch 30 to itshome position, and all of the contacts in the bank contact thereof with the exception of the twenty-fifth contact therein are multipled together. a.

The allotter 50, as shown in Fig. 2, comprises a plurality of relays R300, R,3I0, R320, R330, R340, R350 and R360 and a thermostatic device T326. These relays in the allotter 50 are oper- .ated in a manner more fully described subseone of the trunk circuits does not find a calling' authorized subscriber line within a predetermined time interval, in a manner more'fully described subsequently.

Also, an arrangement comprises a number of chain switches, two of whichare illustrated at 302 and 306, in Fig, 2, are provided forthe purpose of varying the sequence of first-choice local links assigned by the allotter 50 to the use of calling subscriber lines.

Also, it is noted that the conductors of the subscriber lines and information trunk are respectively multipled together between the iinder. and connector switches 22 and 23, respectively, of the local link 2| by way of the multiple 215. Further, this multiple 215 extends to the finder and connector switches of the other links, thereby to render the finder switch of each local link accessible to each subscriber line and the information trunk. Also, it is noted that the connector. switchesv 2 2 ofthe local link 2|, and the inder-connector switch 30.0f the first trunk circuit 60, have access tov thel subscriber lines b y way of the trunk line'200. Also, each of the other local linksv and trunk circuits have access to the subscriber lines by way of this trunk line.

'substation to substation calls A callfwhich is to be extendedy from onesubscriber substation to another is'initiated at the calling lsubstation by removing the telephone receiver the'r'eat from its hook. For example, in extending a call from the authorized subscriber substation A to the semiauthorized subscriber substation B, the call is rst initiatedl at the sub- I station A by removing the telephone receiver thereat from its hook. thereby to complete a bridging path including the receiver` of the telephone instrument between the line'conductors 'C408 and C409 of the Subscriber line 403 individual to the substation A. When this bridge path is completed between the line conductors of the subscriber line 403. a circuit is completed for energizing the combined line -and cut-off relay R390, individually associated with the subscriber line 403, which extends from battery at the lower terminal of the intermediate winding of R390 by way of the intermediate winding of R390, the bridge path between the line conductors of the subscriber line 403, the start conductor C4I8, the winding of the relay R340 in the allotter 50 and the control conductor C204 to ground in the assigned one ofthe local links. Assuming that the illustrated local link 2| is the link assigned, the circuit for energizing the intermediate winding of R390 extends from ground at the armature -RAI5I5 of the relay RI50 in the local link 2| and the back contact associated therewith by way of C204, RA324, the winding of the relay R340 in the allotter 50, C4I8, RA39I, RA43I and the back contact associated therewith, C409, the bridge path between C409 and C408 at the vsubstation A, C408, RA432 and the back contact associated therewith, RA392 and the intermediate winding of R390 to battery.

When energized over the above-traced circuit, the relay R390 partially operates and the relay R340 fully.operates. The partial operation of the relay R390 closes the vX contacts associated with the armatures RA393 and RA394 thereof, thereby to apply 'battery potential by way of the intermediate and upper windings of R390 and RA393 to the start conductor C4|9 and v to apply battery potential by wayV of the lower winding of R390 and RA394 to the control conductor C203.

Upon operating, the relay R340 completes at RA34I, an obvious circuit for energizing the relay R350 in the allotter 50. When energized, the relay R350 operates to interrupt, at RA352, a circuit connection between the start conductor C4|9 and the winding of the relay R300 in the allotter 50, thereby to prevent operation of the relay R300 and the consequent operation of the allotter 50 incident to the initiation of a call at one ofthe subscriber substations, which is to be routed by way of an outgoing trunk line extending to the central exchange 20, and completes at RA35| a path for applying ground potential to the start conductor C4I6. -The application of battery potential to the control conductor C203 marks the subscriber line 403 as a calling line in the contact bank 214 of the rotary switch 212 of the finder switch 22 of the local link 2|. The application of ground potential to the start conductor C4|6 completes a circuit for energizing in multiple the relay R|30 in the local link 2| and the thermostatic device TI60. The circuit for energizing the relay R|30 extends from ground at RA35I by way of the switch springs 308 and 301 of the chain switch 306, C2I0, C228 and the twentyiifth or home contact in the Contact bank 246 of the rotaryv switch 244 of the connector switch 23 of the local link 2|, the associated wiper 245, C226, RAI I4, RAI43 and the back contact associated therewith, the resistor |19 and the upper winding of R| to battery; and the circuit for energizing the thermostatic device TI60 extends from the grounded conductor C2I0 by way of the 76 Winding of T160 to battery. The rotary switch 244 is included in the connector switch 23, the latter switch forming apart of thelocal link 21. When energized over the above-traced circuit, the relay RVoperates to prepare at RA13I a circuit, traced hereinafter, for energizing the motor M111 associated with the iinder switch 22, prepares at RA132 and the front contact associated therewith a point in a circuit, traced hereinafter, for energizing the relay R140, interruptsat RA133 a point in a circuit, traced hereinafter, for energizing the relay R110, and completes at RAI34 a path for applying ground potential to the wiper 213 of the rotary switch 212. The path for applying ground potential to the Vwiper 213 of the rotary switch 212 extends from ground at RAI34 by way of the intermediate winding of R150, RA14I and C233 to the wiper 213. When the circuit fo-r energizing the motor M111 is prepared at RA131, a circuit is completed for initiating the operation of the common equipment, not shown, associated with the local link 2 I. 'This circuit extends from battery at the motor M111 by way of the winding of M111, RAI31, C221, the twenty-fifth or home contact in the contact bank 242 of the rotary switch 240, the associated wiper 241, C222 and RAI51 to the pulse ground lead C119. This application of battery potential to the pulse ground lead C119 initiates the operation of the common equipment as previously noted, thereby to cause the common equipment to transmit ground pulses by way of the pulse ground lead C119, over the above-traced circuit through the Winding of the motor M111 to battery. These ground pulses energize the motor M111 causing intermittent operation thereof and the consequent step-by-step rotation in a clockwise direction of the wipers of the rotary switches 260, 264, 268 and 212 of the finder switch 22.

The intermittent operation of the motor M111 drives the wipers of the rotary switches of the finder switch 22 step by step until the contact in the contact bank 214 of the rotary switch 212 terminating the control conductor C203 and marking the subscriber line 403 is encountered by the associated wiper 213, at which time a circuit for energizing the relay R390 and the relay R150 in series is completed. This circuit extends from ground at RAI34 by way of the intermediate winding of R150, RAI41, C233, the wiper 213 of the rotary switch 212, the contact in the associated contact bank 214 terminating the control conductor C203, C203, RA394 and the lower winding of R390 to battery. When energized over4 the above-traced circuit, the relay R150 operates to interrupt, at RAI51, the short circuit around the resistor 112, thereby tol include this resistor in the circuit for energizing the motor M111. This resistor has a sufficiently high resistance to prevent the ground pulses on the pulse ground lead C119 from being effective to cause the motor M111 to be operated, thereby to arrest further operation of the finder switch 22. The application of battery potential through the winding of the motor M111 by way of the previously traced circuit including the resistor 112 to the pulse ground lead C119 is eective to maintain the common equipment in operation. 4 Upon operating, the relay R150 also interrupts at RA152 a point in a circuit, traced hereinafter, for energizing the relay R110 and completes at RAI53 a circuit for energizing the relay R140,` the latter circuit extending from ground at RAI53 by way of RA132 and the front contact associated therewith and the winding of R to tiple connected upper and intermediate windings of the relay R are included in .a circuit including the lower winding of the relay R390, one path of this circuit extending from ground at RAI34 by way of the upper winding of R150 and RA155 to RAI54, and the other path extending from ground at RAI34 by way of the intermedi ate winding of R150 to RAI54, and the circuit extending from RAI54 by way of C233, the wiper 213 of the rotary switch 212, the contact in the associated contact bank 214 terminating the control conductor C203, C203, RA394 and the lower winding of R390 to battery. The upper wind ing of the relay R150 is of relatively low resistance, thereby reducing the resistance of the circuit for energizing the lower winding of R390 and causing the relay R390 to be fully energized. Also, this application of ground potential to the wiper 213 of the rotary switch 212 in engagement with the contact in the associated contact bank 214 terminating the control conductor C203 of the subscriber line 403 marks the subscriber line 403 as busy to the connector switches of the other local links by Way of the multiple 215 extending between the nder and connector switches of the local links. Further, the relay R150 interrupts, at RA156 and the back contact associated therewith, the previously traced circuit for energizing the relay R340 in serieswith the intermediate winding of the relay R390 and completes at RAI56 and the front contact associated therewith, a circuit. traced hereinafter, for energizing the relay R100.

When the relay R390 is fully energized, it fully operates to interrupt at RA391 and at RA392 further points in the circuit for energizing in series the relay R340 and the intermediate winding of R390. When the circuit for energizing the relay R340 is interrupted, this relay restores to interrupt at RA34I the circuit for energizing the relay R350, causing the latter relay to restore. Upon restoring, the relay R350 interrupts at RA351 the'path for applying ground potential to the start conductor C416, thereby to render the allotter 50 available for further use by the other subscriber substations. Further, the relay R350 prepares at RA352 a point in the circuit for energizing lthe relay R300 thereby conditioning the allotter 50 to be operable incident to the initiation of a call at one of the subscriber substations which is to be extended by way of a trunk line to the central exchange 20.

Also, upon operating, the relay R150 connects Yat RAI51 and at RA158 the relay R130 across the switch 264, the contact in the associated contact bank 266 terminating the positive line conductor of the subscriber line 403, the multiple 215 between the finder switch 22 and the connector switch 23, the trunk conductor 200, the positive line conductor C409 of the subscriber line 403,

RA43I, C409, the bridge at the substation A be- 75 lso line conductor C409 of the subscriber line 403, the trunk line 200, the multiple 216 between the connector switch 23 and the finder switch 22, the

contact in the contact bank 262 of' the finder' switch 260 terminating the negative line conductor of the subscriber line 403, the associated wiper 26|, RAI23, RAI51, and the upper winding of RI30 to battery. Finally, the relay RI50 prepares at RAI59 a circuit, traced hereinafter, for projecting busy tone current over the subscriber line 403 to the substation A in the event the called subscriber substation is busy.

When the relay RI40 is energized over the previously traced circuit, it operates to interrupt at RAI4I a point in the original circuit for energizing the relays RI50` and R390, a path being completed around this point at this time at RAI54, and applies at RAI42 multiple ground to the lower terminal of the upper winding and the upper terminal of the intermediate winding of the relay RI50, thereby to insure that the relays RI50 and R390 are maintained in their operated positions during the impulsing period. Further, the relay RI40 completes at RAI44 a connection between the start conductor C4I6 and the control conductor C423, the latter control conductor extending to the second local link, thereby to render another local link available to the use of a subscriber substation initiating a lcall. This connection extends from the start conductor C4I6 by way of the switch springs 308 and 301 of the Ichain switch 306,' C2I0, RAI, C2II and the switch springs 305 and 303 of the chain switch 302 to the control conductor C423. The previously noted circuit for energizing the relay RI00 extends from ground at RAI56 and the front contact associated therewith, by way of RAI I5, the lower and upper windings of RI00, C225, the

'wiper 249 of the rotary switch 248, the twentyfifth or home contact in the associated contact bank 250, C224 and the upper winding of RI I0 to battery. When energized over the above-traced circuit, the relay RI00 operates. However, the relay RI I0 does not operate, due to the high series resistance of this circuit.

Upon operating, ,the relay RI00 completes at RAI 02 a path for short-circuiting the lower winding thereof, this path extending from the upper terminal of the lower winding of RI00 by way of the lower winding of RI00, RAI I5 and RAI02 to the upper terminal of the lower winding of RI00, and prepares a point at RAIOI in a circuit, traced hereinafter, for energizing the relay RI20. When the lower. winding of the relay RI00 is short-circuited, the series resistance ofthe circuit for energizing the relay RIIO is considerably reduced thereby to cause the relay RI I0 to operate. Upon operating, the relay RI I0 completes at RAI I3 a circuit for energizing the relay RI20, this circuit extending from ground at RAIOI by way of RAI I3 and the lower winding of RI20 to battery. Further, the relay RI I0 prepares at RAI I I a holding circuit, traced hereinafter, for itself, prepares at RAI I6 a path for short-circuiting the relay RI00, tracedl hereinafter, prepares at RAI I2 and the front contact associated therewith a circuit, traced hereinafter, for energizing the motor MI10 associated with the connector switch 23, interrupts at RAI I4 a point in the original circuit for energizing the relay RI30, and interrupts at RAI I5 a point in the short-circuit around the lower winding of the relay RI 00.

When energized over the above-traced circuit, the relay RI20 operates first to close the X contacts associated with its armature RAI22,

thereby tov complete a holding circuit for itself extending from ground at RAIOI by way of RAI22, and the lower winding of RI20 to battery. Subsequently, the relay RI20 operates to interrupt at RAI 2| a point in a circuit, traced hereinafter, for energizingthe motor MI10 in order to cause the motor MI10 to drive the connector switch 23 back into its normal or home position, interrupts at RAI 23 a point in the path for short-circuiting the resistor |15, interrupts at RAI24 a point in the path for short-circuiting the resistor |18, interrupts at RAI25and the back contact associated therewith a point in a path, traced hereinafter, for projecting ringing current over a called subscriber line, and completes at RAI26 a circuit for returning dial tone current over the calling subscriber line 403. The circuit for returning dial tone current over the subscriber line 403 extends from the ungrounded terminal of a source of dial tone current, not shown, by way of the dial tone lead CI18, the condenser I14, the twenty-fifth or home contact in the contact bank 258 of the rotary switch 256, the associated wiper 251, C230, RAI 04, RAI26 and the front contact associated therewith, C230', the wiper 26| of the rotary switch 260, the contact in the associated contact bank 262 terminating the negative conductor of the subscriber line 403, the multiple 215,

the trunkline 200, the negative conductor C408 of the trunk line 403, RA432 and the back contact associated therewith, C408, the bridge including the receiver of the telephone instrument at the substation A across C408 and C409, C409, RA43I and the back contact associated therewith, the positive conductor C409 of the subscriber line 403, the trunk line 200, the multiple 215, the contact in the contact bank 266 of the rotary switch 264 terminating the positive conductor of the subscriber line 403, the associated wiper 265, C23 I, the resistor I 16, RAI 58 and the lower winding of RI 30 to ground. The dial tone produced by the dial tone current in the receiver of the telephone instrument at the substation A indicates to the subscriber thereat that a local link has been seized and that the first digit of the directory number of the called subscriber line may be dialed.

The subscriber at they substation A then dials the first digit of the directory number of the called subscriber line at the dialing mechanism thereat, `thereby to transmit a first series of impulses by way of the subscriber loop'circuit to the relay RI30. impulses in the usual manner, restoring each time the loo'p circuit is interrupted and operating each timev the loop circuit is completed. Each time the relay'RISlI restores, it interrupts 'at RAI32 and the front contact associated therewith the energizing'circuit of the relay RMD and com` pletes at RAI32 and the back Contact associated therewith the holding circuit of the relay RIIO. The holding'circuit of the relay RIIO extends from ground at RAI53 by way of RAI32 and the back Contact associated therewith, RAI I I and the lower Winding of RI I0 to battery. On the other hand, each time the relay RI30 operates, it completes at RAI32 and the front contact associated therewith the `circuit forv energizing the relay RI40 and interrupts at RAI32 and the back contact associated therewith the holding circuit of the relay RI I0. Thus, during the impulsing pe-v riod, the relays RI I0 and RI40, being of the slowto-release type, remain operated. On the first pulse of the first series of impulses, when the re- The relay RI30 follows the dialed lay RI3|I restores, it completes at RAI32 and the back contact associated therewith a circuit i'or energizing the motor MI'III, interrupts at RAI3I a point in the circuit for energizing the motor MIII, and completes at RAI33 a path for shortcircuiting the relay RIM). The path for shortcircuiting the relay RIDO extends from ground at RAIOI by way of RAI33, RAI I5, C224, the twentyifth or home contact in the contact bank 250 of the rotary switch 248, the associated Wiper 249, C225, the upper winding of RIIIU, RAIIIZ and RAI56 and the front contact associated therewith to ground, thereby to cause the relay RI to restore. Upon restoring, the relay RIUU interrupts at RAI 02 la further point in its energizing circuit and a further point in the circuit for shortcircuiting the lower winding thereof, and interrupts at RAIDI a point in the circuit for energizing the relay RI20, thereby to cause the latter relay to restore.

Upon restoring, the relay RI2Yprepares at RAI2I a further point in a circuit, traced hereinafter, for energizing the motor MIII), thereby to cause the motor to operate to drive the connector switch 23 back into its normaler home position. Further, the relay RI20 interrupts at RAIZ! a further point in its holding circuit, completes at RAI23 a point in the path for short-circuiting the resistor I'IS, completes at RAI24 a point in the path for short-circuiting the resistor |16, interrupts at RAI26 and the front contact associated therewith a point in the circuit for returning dial tone current overthe loop circuit extending to the calling substation A, and prepares at RAI25 and the back contact associated therewith and at RAI26 and the back contact associated therewith points in a circuit, traced hereinafter, for projecting ringing current over the called subscriber line. 'I'he circuit for energizing the motor MIII) extends from ground at RAI53 by way of RAI32 and. the back contact associated therewith, RAI i2 and the iront contact associated therewith, and the winding of M I to battery. When energized over the abovetraced circuit, the motor Milli operates to condition the wipers of the rotary switches 240, 244,

248, 252 and 256, comprising the connector switch 23 to be rotated one step in a counterclockwise direction. Upon the rst reoperation of the relay RI30, the above-traced circuit for energizing the motor MI'I0 is interrupted causing the motor MIIU to restore and drive the wipers of the rotary switches comprising the connector switch 23 one step in a counterclockwise direction. When the wiper 251 of the rotary switch 256 is stepped into its first position, the twenty-fth or home contact in the associated contact bank 258 is disengaged, thereby to interrupt a further point in the circuit for returning dial tone current over the loop circuit including the calling subscriber line 403. When the wiper 249 of the rotary switch 248 is stepped into its iirst position, the twentyiifth or home Contactin the associated Contact bank 250 is disengaged, thereby to interrupt the original circuit for energizing the relay RIID. When the wiper 245 of the rotary switch 244 is stepped into its first position, the twenty-fifth or home contact in the associated contact bank 246 is disengaged, thereby to interrupt a further point in the original circuit for energizing the relay RI30. When the wiper 24| of the/rotary switch 240 is stepped into its rst position, the twentyfth or home contact in the associated contact bank 24| is disengaged, thereby to interrupt a point in the circuit for energizing the motor MI 'Il associated with the finder switch 22. Also, when the wiper 24| of the rotary switch 240 is stepped into its first position, it engages the rst contact in the contact bank 242, thereby to prepare a circuit, traced hereinafter, for 'energizing the motor MI'ID, thereby to cause the motor MI'IO to drive the connector switch 23 back into its normal or home position. The relay RI30 follows the impulses dialed at the substation A, thereby to cause the motor MI'IU to be intermittently energized. The intermittent energization of the motor MI'I0 causes the motor MI`I0 to /drive the rotary switches comprising the connector switch 23 step by step in a counterclockwise direction.

The subscriber lines terminating at the con- -nector switch 23 are arranged in three groups.

The first group includes nine subscriber lines vto which the directory numbers between 1 and 9 are assigned. The second group includes nine subscriber lines to which the directory numbers between 01 and 09 are assigned. The third group includes three subscriber lines and an information trunk to which the directory numbers between 001 and 004 are assigned, the directory number 004 being assigned to the information trunk. Assuming that the called subscriber line is arranged in the second group, the first digit dialed at the'substation A is 0. Thus, at the conclusion of thei'lrst digit the wipers of the rotary switches comprising the connector switch 23 occupy their .tenth positions and engage the tenth contacts in the respective associated contact banks. In the contact bank 250 of the rotary switch 248, it will be noted that the tenth, twentieth and twenty-fifth contacts are multipled together and connectedto the conductor C224. At the conclusion of the rst digit dialed, the relay RI30 is reoperated to interrupt at RAI32 and the back contact associated therewith the hold, ing circuit of the relay RI I0, and remains in its operated position until the next digit of the directory number of the subscriber line is dialed at the substation A. Shortly after the holding circuit of the relay RI I0 vis interrupted, this relay, being of the slow-to-release type, restores. Upon restoring, the relay RI I0 completes at RAI I5 an auxiliary circuit for energizing the relays RIIJI) and RI I0 in series, this circuit extending from ground at RAI56 and the front contact associated therewith by way of RAI I5, the lower and upper windings of RIDU, C225, the wiper 249 of the rotary switch 248, the tenth contact in the associated contact-bank 250, C224 and the upper winding of RIII) to battery. When the relays RIIlIl and RIIIl are energized over the abovetraced circuit, the relay RI00 operates. However, the relay RI I0 does not operate due to the high series resistance of this circuit. Upon operating, the relay RIIII) completes at RAI02 the previously traced circuit for short-circuiting the lower winding of RIIlD, thereby to reduce the series resistance of the circuit for energizing the relay RIIU. 'I'he relay RIIO then operates to complete at RAI I3 the previously traced circuit bank 250 of the rotary switch 248, the associated wiper 249, C225, the upper winding of RI`00,

-RAI02 and RAI and the iront contact associated therewith to ground. When the relay RI00 is short-circuitcd, it restores to interrupt at RAIOI the operating and holding circuits of the relay RI20 causing the latter relay to restore as previously explained. The relay RI30 follows the impulses comprising the second digit dialed at the substation A, thereby to cause intermittent energization oi' the motor MI10 as previously explained. The intermittent energization of the motor MI10 causes the motor to drive the wipers of the rotary switches comprising the connector switch 23 to a position corresponding to the called subscriber line. At the conclusion of the second digit dialed at the substation A, the Wipers 249, 258 and 251 of the rotary switches 248, 252 and 256 engage the contacts in the associated contact banks 250, 254 and 258 respectively terminating the control, positive and negative conductors of the called subscriber line 402.

The subsequent operation of the local `link 2| depends upon whether the called subscriber line is idle lor busy. Assuming that the called subscriber line is busy, ground potential through a low resistance is present upon the control conductor thereof, terminating at the contact in the Contact bank 250 of the rotaryswitch 248 engaged by the associated wiper 249. This ground potential is derived in a busy link associated with the called subscriber line 402., More particularly, the ground potential is derived in the busy link associated with the busy subscriber line 403 at an armature vcorresponding to the armature RAI42 of the relay RI40 in the local link 2-I, in the event the subscriber line is busy on a call initiated at the.subscribersubstation B, and at an armature corresponding to the armature RAI56 of the relay RI50 in the local link 2l, in the event the subscriber line is busy on Va call initiated at another subscriber substation and extended to the subscriber substation B. This ground potential on the wiper 249 of the rotary switch 248 completes a path for shortcircuiting the relay RI00, subsequent to the restoration of the relay RI I0 shortly after the conclusion of the second digit dialed at the substation A, this path extending from ground potential on the Wiper 249 by way of C225, the upper and lower windings of RI00 and RAI I 5 to ground at RAI56 and the front contact associated therewith. At this time busy tone current is returned over the loop extending to the calling substation A, the circuit for returning busy tone. current extending from the ungrounded terminal of a source of busy tone current, not shown, by way of the busy tone lead CI11, RAI05 and the back contact associated therewith, the condenser I13, RAI59, C23I, the wiper 265 of the rotary switch 264, the contact in the associated contact bank `286 lterminating the positive conductor of the ing the receiver of Vthe telephone instrument across C409 and C408, at `the substation A, RA432, the negative conductor .C408 of the subscriber line 403, the trunk line 200, the multiple 215, the v contact in the contact bank 262 of the rotary switch 260 terminating the negative conductor of the subscriber line 403, the wiper 26|, C230', RAI23, RAI51 and the upper Winding ofv RI30 to lstation A camps on the busy called battery. The resultant busy tone produced by the receiver oi' the telephone instrument at the substation A indicates to thesubscriber thereat that the desired connection can not immediately be had due to the busy condition of the called subscriber line. At this time, the subscriber at the substation A may abandon the call and release the apparatus, by replacing the receiver of the telephone instrument at the substation A upon its hook, in a manner more fully described subsequently. or he may wait for the calledsubscriber line to become idle. When the subscriber line becomes idle, the local link 2IA operates to project ringing current over the called subscriber line, provided the subscriber at the subsubscriber line 402.

At the conclusion ofthe second digitldialed at the substation A and after the relay RIIO restores, a circuit .is completed for energizing the relay RI 00 in the event the called subscriber line 402 is idle. This circuit extends from ground at RA|56 and the front contact associated therewith by way of RAI I5, the lower and upper windings of RI00. C225, the wiper 249 of the rotary switch 248, the contact in the associated contact bank 250 terminating the control conductor of the subscriber line 402, the trunk linel200, the control conductor C422 of the subscriber line 402 and. the lower winding of R380 to battery. When energized over the above-traced circuit. the relay R100 operates to complete at RAI02 the previously traced path for short-circuiting the lower winding thereof, thereby to reduce the series resistance of the circuit for 'energizing the relay R380 causing the relay R390 to completely operate. Rl00 marks the control conductor of the called subscriber line 402 as busy to the connector switches of the other links and to the trunk finder-connector switches by the application of ground potential thereto. Upon operating, the relay R380 interrupts at RA38I and at RA382 points in the path for applying battery potential at the lower terminal of the intermediate winding of R380 to the start conductor C4I8 when the call is answered at the substation B, thereby to prevent the nder switch of a local link from being associated with the subscriber line 402 when the call is answered at the substation B. Further, the relay RI00 prepares at RAIOI a point in the holding circuit of the relay RI20 and completes at RAIIJ3 and at RAIIM points in a 'circuit for projecting ringing current over4 terminal of a source of ringing current, lnot shown, by way of the ringing current lead CI06, the upper winding of RI20, RAI25 and the back Contact associated therewith, RAI03, C221, the wiper 253 of the rotary switch 252, the contact in the associated contact bank 254 terminating the positive conductor of the called line 402, the trunk line 200, the positive conductor C4I3 of the subscriber line 402, the bridge including a ringer and a condenser at the substation B across C4I3 and C4I2, the negative conductor C4I2 oi the subscriber line 402, the trunk line 200, the contact in the contact `bank 258 of the rotary switch 256 terminating the negative conductor of the subscriber line 402, the associated wiper 251, C230 and vRAI04 to ground at RAI26 and the back contact associated therewith. A portion of this ringing current'is returned over the looD extending to the calling substation A in order to provide ring-back tone at the receiver of the -tele- Y phone instrument thereat.

'I'he circuit for returning ring-back tone current to the calling substation A extends from the ringing current lead C|06.by way of the upper winding of R|20, RA|25 and the back contact associated therewith, RAIUS, C221, C229, RA|06 and the front contact associated therewith, the condenser |13, RAl59, C23|, the wiper 266 of the rotary switch 264, the contact in the associated contact bank 266 terminating the positive conductor of the calling subscriber line 403, the multiple 216, the trunk line 200, the positive conductor C409 of the subscriber line 403, RA43I, C409, the bridge including the receiver oi' the telephone instrument at the substation A across C409 and C408, C408, RA432, the negative conductor C406 of the subscriber line 403, the trunk line 200, the multiple 215, the contact in the contact bank 262 of the rotary switch 260 terminatingthe negative conductor of the subscriber line 403, the associated wiper 26|, C230', RAl23, RA|61 and the upper winding of R|30 to battery. 'I'he ring-back tone produced in the receiver oi' the telephone instrument at the substation A indicates to the subscriber thereat that ringing current is being projected over the called subscriber line. The ringing current projected over the subscriber line 402 operates the ringer at the called substation B, thereby to indicate to a subscriber thereat that this substation is being called.

When the subscriber at the substation B answers the call by removing the receiver of the telephone instrument thereat from its hook, a bridge including the telephone instrument at the substation B is connected across the line conductors C4|2 and C4|3 of the called subscriber line 402. This bridge across the line conductors C4|2 and C4I3 of the called subscriber line 402 completes a low resistance circuit substantially identical to the circuit for projecting ringing current over the called subscriber line 402, thereby to cause the relay R|20 to be eilectively energized. The relay R|20, being of the slow-tooperate type, operates shortly thereafter. First, the relay R|20 operates partially to close its X contacts associated with the armature RAI22, thereby to complete its holding circuit. The relay R|20 then completely operates to interrupt at RA|26 and the back contact associated therewith and at RA|26 and the back contact associated therewith, the circuit for projecting ringing current over the called subscriber line 402 and the circuit for returning ring-back tone current over the calling subscriber line 403. Further, the relay R|20 interrupts -at RA|2| a point in the path for applying battery potential at the motor M|10 to the pulse'ground lead CH3, thereby to cause the operation of the common equipment connected to the pulse ground lead C|19 the associated contact bank 264 terminating the positive conductor of thelcalled subscriber line 402, and from the negative line conductor ot the calling .subscriber line 403 terminating at the contact in the contact bank 262 of the rotary switch 260 engaged by the associated wiper 5 26|, by way of the wiper 26|, C230', RA|26 and the front contact associated therewith, RAI04 and C230 to the wiper 261 of therotary switch 266 engaging the contact in the associated conl tact bank 268 terminating the negative conduc- 10 tor of the called subscriber line 402, the telephone instrument at the calling substation A being bridged across the positive and negative line conductcrs of the subscriber line 403, and the telephone instrument at the called substation B be- 15 ing bridged across the positive and negative line conductors of the subscriber line 402. Finally, the relay R|20 interrupts at RA|23 the path-for short-circuiting the resistor |16 and interrupts at RAI24 the path for short-circuiting the re- 5 tending to calling and called subscriber substau tions, this circuit extending from ground at the lower terminal of the lower winding of RI by way of the lower winding of R|30, RAIII and the resistor |16 to C23| and from battery at the upper terminal of the upper winding of R|3l by way of the upper winding of R|30, RA|61 and the resistor |16 to C230', the conductors C230' and C23| being connected together by way of the loop circuits extending to the called and calling substations.

The release of an established connection between the calling substation A and the called substation .B is under the control of the lastsubscriber to replace his telephone instrument upon its hook. When the last subscriber replaces his telephone instrument upon its hook, the loop circuit including the upper and lower windings of the relay R|30 is interrupted, thereby to cause -the relay R|30 to restore. Upon restoring, the relay R|30 interrupts at RAI 32 and the front contact associated therewith the circuit for energizing the relay R|40 and removes at RA|34 the ground potential from the lower and upper terminals of the upper and intermediatev windings, respectively, of the relay R|60. Shortly thereafter, the relay R|40, being of the slowto-release type, restores to remove ground potential at RA|42 from the previously mentioned terminals of the upper and intermediate windings of the relay R|60. thereby to cause the relay R|60 to restore. The relay R|40 also prepares at RA|43 and the back contact associated therewith a point in the path for connecting the upper winding of the relay RI30 by way of 'the twenty-fifth or home contact in the contact bank 246 of the rotary switch 244 to the start conductor C4| 6 and interrupts at RA|44 the connection between the start conductor C4|6 and the control conductor C423 extending to the 66 second link.

When the relay R|40 interrupts at RA|42 the path for applying ground potential to the previously mentioned terminals of the upper and intermediate windings of relay R|60, the circuit for 70 energizing the relay R390 associated with the calling subscriber 403 is interrupted, thereby to cause the relay R390 to restore. Upon restoring, the relay R390 prepares at RA39| and RA392 points 1n the circuit for operating the relay am 15 in the allotter 50 when the next subscriber substation call is initiated at the substation A. At this time, the apparatus associated with the substation A is completely released for further use. Upon restoring, the relay RI50 interrupts at RAI 56 and the front contact associated therewith the circuit for energizing in series Vthe upper winding of RI and the relay R360 associated with the called subscriber line 402, thereby to cause these relays to restore.' When the relay R360 restores, it prepares at RA30I and RA3 02 points in the circuit for energizing the relay R340 in the allotter 50 when a'call is initiated at the substation B. At this time, the apparatus associated with the substation B is completely released for further use. Further, the relay RI50 prepares at RAI56 and the back contact associated therewith a point in the circuit for energizing the relay R340 .in the allotter 50 when the next subscriber substation call is initiated at one f of the substations.v Also, the relay RI50 interrupts at RAI54 a further point in the circuit for energizing the upper and lower windings thereof, interrupts at RAI55 a further point in the cir-A cuit for energizing the upper winding thereof, interrupts atr RAI'I and at RAI56 points in the circuit for connecting the upper and lower windings of the relay RI30 to the conductors C230' and C23I and interruptsat RAI59 a point in the circuit for returning busy tone over the calling subscriber line. Finally, the relay RI50 completes at RAI5I a point in the path for shortcircuiting the resistor |12.

Upon restoring, the relay RI00 interrupts at RAIOI the holding circuit of the relay RI20 causing the latter relay to restore, interrupts at RAI02 a point in the path for short-circuiting the lower winding thereof and interrupts at RAI03 and at RAI04 points in the connections between the rotary switches 252, 264 and l256, 260, respectively. Finally, therelay RI00 interrupts at RAI05 and the front contact associated therewith a further point in the circuit for returning ring-back tone current over the calling subscriber line and prepares at RAI05 and the back contact associated therewith a point in the circuit for returning busy tone current over the calling subscriber line. Upon restoring, the relay RIZ() completes at RAI2I a circuit for connecting battery potential at the upper terminal of lRIIU by way of the lower winding of RIIO,

RAI52, RAI2I,YC223, the multiple connected contacts in the contact bank 242 Vof the rotary switch 240, the associated wiper 24I, C222 and RAISI to CI'I9. This application of battery pov tential to the pulse ground lead CI'I9 initiates the operation of the common equipment connected thereto and causes the relay RI I0 to be energized over the above-tracedr circuit. When energized, the relay RIIO operates to interrupt at RAI I4 a further point inthe original operating circuit of the relay RI30, thereby to prevent operation of the relay RI30 incident to the operation of the relay R350 in the allotter 50 before the local link 2l is completely released, and completes at RAI II and at RAI I2 and the front contactV associated therewith a circuit for energizing the motor MI10, this circuit extending from the pulse ground `lead CI19 rby way of RAI5I, C222, the wiper 2li voi? the rotary switch 240, the multiple connected contacts in the associated contact bank 242, C223, RAI2I, RAI52,

RAIII, RAII2 and the front contact associated therewith and the winding of MI to battery. 'I'he motor MI10 is intermittently energized by way of the above-traced circuit, thereby to cause intermittent operation thereof. The intermittent operation of the motor MI10 drives the wipers of the rotary switches comprising the connector switch 23 step by step in a counterclockwise direction until these wipers are driven into their twenty-fifth or home positions. When the wiper 24I of the rotary switch 240 is moved into its twenty-111th or home position, the multiple connected contacts in the associated con--v tact bank 242 are disengaged, thereby to interrupt the circuits for energizing the motor MI10 and for energizing the relay RIIO. Thus, operation of the motor MI10 is arrested and the relay RIIO, being of the slow-to-release type. restores shortly thereafter. When the circuits for energizing the motor MI10 and the relay RI I0 are interrupted, operation of the common' equipment connected to the pulse ground lead CIN is arrested. At this time the start lead C4I6 is connected by way of the switch springs 306 and 301 of the chain switch 306, C2I0, C228, the twenty-fifth or home contact in the contact bank 246 of the rotary switch 244, the associated wiper 245, C226, RAI I4, RAI43 and the back contact associated therewith, the resistor |19 and the upper winding of RI30 to battery. Thus, at this time, the local link 2I is completely released and is again in condition to be seized when a subscriber substation call is initiated at one of the substations.

It will be understood that a call initiated at any one of the authorized, semiauthorized or unauthorized subscriber substations will cause the combined line and cut-oil relay individually associated therewith to operate in a manner similar to the operation of the relay R390 and that the allotter 50 will cause the finder switch of a local link to operate and find the calling subscriber line as previously explained. After a local link is associated with the subscriber substation initiating the call, the call maybe extended to any one of the authorized, semiauthorized or unauthorized subscriber substations by dialing at the dialing mechanism at the calling subscriber. substation the directory number of the desired called subscriber substation, the operation of theconnector switch of the local link associated with the calling subscriber line being the same as that previously described.

Also, it is noted that the attendant cabinet 40 has access and is accessible to the local links .by wayof the information trunk 650 in a manner similar to the subscriber-substations. In order to initiate a subscriber substation call at theV attendant cabinet 40 the information trunk switch 593 thereat is operated to its front position, thereby to complete at the switch springs 594 and 505 and the front contacts associated therewith a path for applying battery potential to the start conductor C4I8. This path extends from battery at the lower terminal of the upper winding of the relay R200 by way of the upper winding of R260, RA262, C65I, the switch spring 594 and the front contact associated therewith, C654, RA53I, RA5I2, C651, the impedance 500, C655, the switch spring 595 and the front contact associated therewith, C652, RA28I, C424, and C931 to the start conductor C4I6. 'This application of battery potential tov vthe start conductor C4I8 causes the allotter 50 to operate, thereby to cause the nnder switch oi an idle local link to ilnd the information trunk, as previously explained. A connection between a subscriber substation having a local link associated therewith andV the attendant cabinet may be established by dialing at the dialing mechanism at the substation the directory number of the information trunk 850, thereby to cause the connector switch of the local link to seize the information trunk, as previously explained.

When the nder switch 22 of the local link 2l seizes the calling subscriber line 403, the relay R| is operated as previously explained. Upon operating, the relay R|50 interrupts at RAI56 and the front contact associated therewith the application of ground potential in the rst local link 2| to the control conductor C204. When all of the local links are busy, all of the relays therein corresponding to the relay R|50 occupy their operated positions. Accordingly, ground potential in each local link is removed from the control conductor C204. At this time, when a subscriber substation call is initiated at any one oi' the subscriber substations, the relay R340 in the allotter 50 is not operated due to the removal oi' ground potential in all of the local links from the control conductor C204. Thus, the relay R350 is not operated. When the relay R350 occupies its restored position, the circuit for energizing the relay R300 by way of the start conductor C4I9 is prepared at RA352. Accordingly, outgoing trunk or central exchange calls from authorized subscriber substations may be completed at this time, as such calls do not require the use oi' a local link in their completion.

Authorized substation to central exchange calls A subscriber at an authorized substation may initiate a call to the central exchange without the assistance of the attendant at the attendant cabinet. For example, in initiating a call from the authorized substation A -to the central exchange 20, the subscriber at the substation A momentarily presses or operates the grounding push button 393 of the telephone instrument at the substation A without removing the receiver of the telephone instrument from its hook. When the push button 393 is momentarily operated, a circuit is completed for energizing the relay R390 associated with the subscriber line 403 extending to the substation A, this circuit extending from ground at the push button 393 by way of C408, RA432, RA392 and the intermediate winding of R390 to battery. When the relay R390 is energized over the above-traced circuit, it partially operates to close the "X contacts associated with the armatures RA393 and RA396, thereby to apply battery potential at the lower terminal of the intermediate winding of R390 by way of the intermediate and upper Windings of R300 and RA393 to the start conductor C4l9 and to connect the control conductor C4l1 by way of RA395 and RA396 tothe control conductor C406 of the subscriber line 403. The ap.- plication of battery potential to the start conductor C4I9 completes a circuit for energizing the relay R300 in the allotter 50, this circuit extending from battery potential on the start conductor C4|9 by way of RA352, RA332, RA3I2 and the back contact associated therewith and the winding of R300 to battery. The relay R300, being of the slow-to-operate type, operates shortly thereafter to complete at RA30| a circuit for energizing the relay R320, this circuit extending from ground at RA30I by way of RA3II and the back contact associated therewith and the upper winding of R320 to battery. `vWhen energized over the above-traced circuit. the relay R320 operates to complete at RA32 obvious circuits for energizing the thermostatic device T325 and for energizing the relay R3|0, the circuit for energizing the relay R3|0 extending from ground at RA32I by way of the upper winding of R3|0 to battery. Further, the relay R320 completes at RA323 a circuit for holding the relay R390 operated after the grounding push button 393 is restored, this circuit extending from ground at RA323, by way of RA332, RA352, the start conductor C4I9, RA393 and the upper and intermediate windings of R390v to battery. Further, the relay R320 interrupts at RA324 a point in the circuit for energizing the relay R340 in series with the intermediate winding of the relay R390', thereby to preventoperation of the relay R340 incident to the initiation at one of the subscriber substations of a subscriber substation call before the call from the substation A to the trunk line extending to the central exchange 20 has been completed. Further, the relay R320 completes at RA325 a path for applying ground potential to the control conductor C4I1 connected to the control conductor C406 of the calling subscriber line 403, this path extending from ground at RA325 by way of C4I1, RA395 and RA393 to the control conductor C406. This application of ground potential marks the subscriber line 403 as a calling line in the trunk finder-connector switch of the trunk circuit assigned to the use of the next central exchange call. Assuming that the rst trunk circuit 30 is assigned, the trunk finder-connector switch 30 thereof is thus marked, this path extending from the control conductor C406 of the calling subscriber line 403 by way or the trunk line 200 toV the contact in the contact bank 613 of the 'rotary switch 814 of thevtrunk ilnder switch 30 terminating this control conductor. Finally, the relay R320 completes at RA322 a path for applying ground potential to the control conductor C638 of the first trunk circuit, this path extending i'rom ground at RA322 by way of the lower :vinding oi' R320, TA326, RA33I, and RA333 and the back contact associated therewith to the control conductor C033.

When energized over the above-traced circuit,

the relay R3|0 operates to interrupt at RA3 I I and the back contact associated therewith the orig inal circuit for energizing the relay R320, the relay R320 beingheld in its operated position at this time from battery potential in the first trunk circuit in a manner more fully explained subsequently. Further, the relay R3|0 interrupts at RA3I2 and the back contact associated therewith a point in the circuit for energizing the relay R300, causing the' latter relay to restore, and completes at RA3I2 and the front contact associated therewith a holding circuit for itself, this circuit extending from ground at RA323 by way of RA3I2 and the front contact associated therewith, and the lower winding of R3|0 to battery. Upon restoring, the relay R300 interrupts at RA30| the original circuit for energizing the relay R320.

The application of ground potential on the control conductor C638 causes the first trunk circuit .to be associated with the calling subscriber line 403, this trunk circuit being assigned for use as it is`assumed to be idle. This application of ground potential to the control conductor C638 of the first trunk circuit completes a. circuit for energizing the relay R and the thermostatic device T805, this lcircuit extending from ground at RA322 by way of the lower winding of R320,"I'A326, RA33 I RA363 and the back contact associated therewith, C638, the switch springs 6I3 of the dial-split switch 6|0 at the attendant cabinet 40, C63|, RA113 and C852 to the terminal of the lower winding of R150, one branch of this circuit extending from the lower terminal of the lower winding of R150 'by way of the lower winding of R150 to battery, and the other branch extending from the lower terminal of the lower winding of R150 the relay R150 applies at RA155 multiple ground potential to the start conductor C822, thereby vto prepare a circuit, traced hereinafter, for holding the relay R150 in its operated positionv independently of the restored condition of the relay R330 in the allotter 50. Further, the relay R150 connects the lower winding of4 the relay R120 to the wiper 615 of the rotary switch 614 of the trunk finder-connector switch 30, thereby to prepare a circuit for energizing the relay R120 when the wiper 615 of the rotary switch 610 is operated tothe position of the contact in the associated contact bank 616.terminating the control conductor C406 of the calling line 403. Further the relay R150 applies ground potential atv RA15| to the control conductor C829 of the link line 830 extending between the first trunk circuit and the finder switches of the local finder links. In the case ofthe local link 2|, this path extends from ground at'RA15I by way of the'control conductor C829 of the link line 830 to the contact in the contact bank 210 of the rotary switch 268 .terminating the control conductor of vthe, link line, thereby to mark the Afirst trunk circuit 60 as busy to all of the local links, the finder switch 22 of the local link 2| being multipled to the connector switch 23 thereof and to the finder and connector switches of the other local links. Finally, the relay R150 completes a path for applying battery potential to the pulse ground lead C119, one branch of. this pathextending from battery at the winding of the motor M6|5 by Way of the winding of M6|5 and C625 to RA12 3, another branch of this path extending from battery at' the lower terminal of the upper Winding of R140 and by way of the upper winding of R140 to RA123, and the a counterclockwise direction vover the associated The intermitcontact banks, until the wiper 615 of the rotary switch 614 engages the contact in the associated contact bank 616 terminating the control conductor C406 of the calling subscriber line 403 as marked by ground potential thereon. Also, the ground pulses on pulse ground lead C|19 energize the relay R140 over the path previously traced, thereby to cause operation thereof. Upon operating, the relay R140 completes at RA145 an obvious path for short-circuiting the lower winding thereof, thereby to render the relay R140 slow-to-release. Due to this slow-to-release characteristic of the relay R140, this relay does not restore during the irnpulsing period while the trunk finder-connector switch 30 is hunting the calling subscriber line. Further, the relay R140 interrupts, at RA14| andat RA142, the connections between the trunk conductors C624, C835 and C622, C836, respectively, of the rst trunk circuit 60, the conductors C624 and C622 being connected to the wipers 681 and 683, respectively, of the rotary switches686 and 682. As the positive and negative conductors of the subscriber lines terminate in the contact banks 684 and 688 of the rotary switches 682 and 686, respectively, this disconnection of the conductors C624 and C622 connected to the wipers 681 and 683 of the rotary switches 686 and 682, respectively, from the conductors C835 and C836, re-

spectively, prevents the operation of the trunk `iinder-connector switch 30 from interfering with `completed calls on .the busy subscriber lines as the Wipers of the rotary switches 68,2 and 686 are driven over the associated contact banks. Finally the relay R140 completes at RA144 and the front contact associated therewith a path for connecting the upper and intermediate windings of the relay R120 in multiple for a purpose more` fully explained subsequently, this path extending from the lower terminal of the upper winding of R120 by way of the upper winding of4R120, RA144 and the front contact associated therewith and the intermediate winding of R120 to the lower terminal of the upper winding of R120.

The energization of the thermostatic device T805 causes the thermal responsive element thereof to become heated, which element, after being heated for apredetermined time interval, operates to reconnect at TA806 the control conductor C838 to the control conductor C802, thereby to extend ground potential into the second trunk circuit. This operation of the thermostatic device T805 occurs after a predetermined time interval, thereby to render the second trunk circuit operative tocause the trunk finderconnector switch thereof to operate and find the subscriber line 403 in the event the trunk finderconnector switch 30 of the first trunk circuit 60 does not find the calling line 403 in this predetermined time interval.

When the wiper 615 of the rotary switch 614` is rotated to a position corresponding to the position of contact in the associated contact bank 618 terminating the .control conductor C406 of the calling subscriber line 403, a circuit for energizing the relay R120 is completed, this circuit extending from ground at RA325 by way of CM1, RA395, RA396, the control conductor C406 of the subscriber line 403, the trunk line 200, the contact in the contactbank 616 ,of the rotary switch 614 terminating the control conductor C406 of the subscriber line 403, .the associated above-traced circuit, the relay R120 operates to interrupt at RA123 the path for energizing the motor M6I5 and the relay R140 from the pulse ground lead CI19, thereby to cause further peration of the motor M6I5 to be arrested and to cause the relay R140 to restore shortly thereafter. Further, the relay R120 completes at RA124 a circuit for illuminating the answer and supervisory lamp 564 located at the attendant cabinet 40, this circuit extending from ground at RA124by way of C838, RA902 and the back contacty associated therewith, C846, the resistor 184, RA182 andthe back contact associated therewith, C64I, the switch spring 51| of the night l5 SWitCh 510 and the lamp 584 to battery. Itwill be noted that the circuit for illuminating the answer and supervisory lamp 564 includes the resistor 184, thereby causing the lamp 564 to be illuminated dimly. This illumination oi the answer and supervisory lamp 564 indicates to the attendant at theattendant cabinet 40 that the iirst trunk circuit 60 is busy. Further, the relay R120 completes at RA121 a circuit for energizing in series the lower winding of the relay R390 associated with the calling subscriber line 403, and the multiple connected upper and intermediate windings of the relay R120. This circuit extends from ground at RA154 by way of C843 to. RA121, one branch extending from 80 Ram by way of RAM and the front Contact associated therewith and the upper Winding of R120 to CSIS, and the other branch extending from RA121 by way of the intermediate winding of R120 to C6I9, the circuit further extending from C6I9 by way of the wiper 618 of the rotary switch 618, the contact in the associated contact bank 680 terminating the control conductor C401 of the subscriber line 403, the trunk line 200, the control conductor C401 of the subscriber line 403, and the lower winding of R390 to battery. When energized over the above-traced circuit the relay R390 operates completely.

Upon operating completely, the relay R390 interrupts at RA39I and at RA392 points in the circuit for energizing the relay R340 in the allotter 50, thereby to prevent operation of the relay R340 and the consequent association of a local link with the calling subscriber line 403 when the receiver of the telephone instrument at the substation A is removed from its hook. Further, the relay R390 interrupts at RA395 a point in the original circuit forenergizing the lower winding of the relay R120. The application of ground potential through the multiple connected upper 55 and intermediate windings of the relay R120 and the rotary switch 618 to the control conductor C401 of thesubscriber line 403 marks the subscriber line 403 as busy in the other trunk nderconnector switches and in the local links. 50 Further, upon operating, the relay R120 completes at RA129 a circuit for energizing in series the relay R110 and the thermostatic device T8I0, this circuit extending from ground at TA8II by way of C86I, RA129, C860, the winding of T8I0, RA161 and the back contact associated therewith, C118 and the winding of R110 to battery. Finally, the relay R120 completes at RA12I a. path for applying ground potential to the negative line conductor of the calling subscriber line 403 and at RA122 and the front contact associated therewith a path for applying direct generating potential from the generator lead C800 by Way of the lower winding of R160, to the positive line conductor of the subscriber line 403. The application of ground potential to the negative line conductor and the application of direct generator potential to the positive line conductor of the calling subscriber line 403 completes a circuit for operating the ringer at the substation A, this cir- 5 cuit extending from ground at RA162 and the back contact associated therewith, by way of C860, RA12I, C624, the wiper 881 of the rotary switch 68E/'the contact in thel associated contact bank 688 terminating the negative line conductor 10v oi the subscriber line 403, the ytrunk line 200, the negative line conductor C408 of'the subscriber line 403, RA432, C408, the bridge between C408 and C409 including a ringer and a condenser at the substation A, C409, RA43I, the positive line l5 conductor C409 of the subscriber line 403, the trunk line 200, the contact in the contact bank 684 of the rotary switch 682 terminating the positive line conductor oi the subscriber line 403, the associated wiper 883, C622, RA122 and the 80 front contact associated therewith, C86I, RA163 and the back contact associated therewith, C119, the lower winding of R160, RA1 I4 and the back contact associated therewith, and the directgenerator lead C800 to the ungrounded terminal of 25 l the generator, the other terminal oi the generator being connected to ground. 'I'he operation of the ringer at the substation A indicates to the subscriber thereat that a trunk circuit has been associated with the subscriber line 403 ex- 30 tending to the subscriber substation A and is available for use.

Upon restoring the relay R140 prepares at RAMI and at RA142 the transmission circuit between the positive and negative conductors of the subscriber line 403 and the trunk conductors C835 and C836 of the iirst trunk circuit 60. At this time the trunk conductor C624 connected to the negative line conductor of the subscriber line by way of the rotary switch 686 is connected 40 by way of RAI4I and the condenser 8I2 to the trunk conductor C835, and `the trunk conductor C622 connected to the positive lline conductor of the subscriber line by way of the rotary switch 682 is connected by way ot the condenser 8| 5, 48 RA142 and the condenser 8I3 to the trunk conductor C836. When the relay R is energized over the previously-traced circuit, it operates to complete at RA11I a path for applying ground potential to the control conductor C401 of the 60 subscriber line 403, thereby to retain energized the intermediate winding of the relay R subsequent to the restoration of the relay R150.A This circuit extends from ground at the switch spring 605 oi the connect switch 600 located at 65 the attendant cabinet 40 by way of the switch spring 606, C630, RA11I, C843, RA121, the intermediate winding of R120, C6I9, the wiper 618 of the rotary switch 618 terminating the control conductor C401 of the subscriber line 403. 60 the trunk line 200, the control conductor C401 of the subscriber line 403 and the lower winding of R390 to battery. This application of ground potential to the control conductor C401 oi the subscriber line 403 marks the subscriber line 403 05 as busy, as previously explained. Further the relay R110 applies ground at RA115 to the conductor C635 for a purpose more fully described subsequently and interrupts at RA113 the circuit for energizing the multiple connected 70 lower winding of the relay R and the thermostatic device T805 in series with the lower winding of the relay R320 in the allotter 50, thereby to cause the relays R150 and R320 to restore. Further, the relay R110 completes at RA116 a 76 

